Background Anaesthetists are responsible for the management of the airway in patients with unstable cervical spine (C spine). The optimal tracheal intubation technique for patients with potential C spine injury remains controversial. Videolaryngoscopes are used in an attempt to balance the need to limit cervical motion and overcome the difficulty of obtaining laryngeal views especially with manual in-line stabilization or cervical collar.Aim The current study aimed to compare the degree of C spine movement during intubation using different devices, Macintosh direct laryngoscope, C-MAC D-Blade videolaryngoscope and flexible intubation video endoscope (FIVE), in anaesthetized patients with normal airway and simulated C spine immobilization.Patients and methods This study was carried out on 45 adult patients scheduled for radiographic procedures under general anaesthesia with endotracheal intubation (ETT). Patients were randomly divided into three equal groups (15 patients each) using the sealed envelope technique: group M (Macintosh direct laryngoscope), group D (C-MAC D-Blade) and group F (FIVE). C spine movement was recorded with continuous fluoroscopy at 3–8 frames/s using a digital videofluoroscopy unit during both laryngoscopy and intubation to capture the maximal extent of C spine movement. The following parameters were evaluated: age, BMI, airway score, haemodynamic parameters, glottic view grade (Cormack and Lehane), time to successful ETT insertion and maximum segmental spine motion.Results The three studied groups were matching as regards age, BMI and airway score. Heart rate and mean arterial blood pressure observed after insertion of the ETT were statistically higher in group M compared with groups D and F. However, there were no significant differences in mean observed HR and mean arterial blood pressure between groups D and F at all time intervals. The Macintosh (group M) had significantly higher C and L grades than the two other devices in groups D and F. There was no significant difference in C and L grades attainted by the D-Blade in group D and the FIVE in group F. D-Blade had significantly shorter intubation time compared with Macintosh and FIVE. Macintosh direct laryngoscope resulted in significantly greater cervical movement at all measured motion segments compared with D-Blade and FIVE. Meanwhile, FIVE caused significantly less motion compared with D-Blade.Conclusion In patients with potential C spine injury and cervical immobilization, D-Blade results in less cervical motion, better glottic views and shorter intubation time compared with Macintosh laryngoscope. Flexible intubation scope causes the least cervical motion but with the longest intubation time.

Anaesthetists are responsible for the management of the airway in patients with unstable cervical spine (C spine). Tracheal intubation must be performed with extreme care in patients with suspected C spine pathology to prevent cord damage [1]. The optimal tracheal intubation technique for patients with potential C spine injury remains controversial [2]. The flexible intubation scope (FIS) has long been considered the ‘gold standard’ for intubating patients with C spine abnormalities requiring spine immobilization [3],[4]. Although FIS intubation may expose C spine to the least traction, this procedure requires significant skill [5],[6],[7], and a cooperative patient if it is to be performed on an awake patient. For the anaesthetized patient, however, the FIS and the manoeuvres commonly used to enlarge the posterior pharyngeal space such as jaw thrust and tongue pull are associated with varying degrees of cervical motion [5],[8],[9]. Its potential may be limited by lack of expertise, blood or secretions in the airway, lack of cooperation in awake patients and the additional time required to prepare for and execute the procedure. Interestingly, there is no scientific evidence supporting better clinical outcomes in patients with C spine disease who were intubated with an FIS compared with other commonly used airway devices [10]. In the emergent situation, however, direct laryngoscopy with manual in-line stabilization (MILS) by an assistant in the anaesthetized patient is most commonly used [11], as it is quicker, less affected by blood, secretions and vomitus present in the airway and does not require patient collaboration [2]. However, the use of MILS or semirigid cervical collar to protect the C spine significantly limits cervical extension to a degree that makes intubation difficult, lengthening the duration of intubation or causing repeated intubation interventions. Moreover, a cervical collar reduces mouth opening leading to difficulty in intubation [12],[13],[14].

A more accessible alternative to the FIS would be advantageous for the emergency airway management of patients with C spine disease. Indirect laryngoscopy techniques have been studied in an attempt to balance the need to limit cervical motion and overcome the difficulty of obtaining laryngeal views when MILS or cervical collar are applied. Videolaryngoscopes may be easier to learn than FIS and may offer improvement in terms of intubation difficulty compared with direct laryngoscopy. As such, their use has grown for the management of patients with C spine precautions [8].

Patients and methods

This study was conducted in Alexandria Main University Hospital, Alexandria University, Egypt, after approval of the Local Ethical Research Committee and having written informed consent from all patients. A total of 45 adult patients, ASA I and II, scheduled for radiographic procedures under general anaesthesia with endotracheal intubation (ETT) were enroled in the study. The sample size was approved to be sufficient by the Department of Statistics, High Institute of Public Health, Alexandria University, Egypt. Exclusion criteria were BMI more than 30 kg/m2, previous neck surgery, clinical or radiographic evidence of C spine abnormality, mouth opening less than two fingers and airway score (AWS) of at least 4 evaluated by El-Ganzouri multivariate risk index [15],[16],[17]. Studied patients were randomly divided into three equal groups (15 patients each) using the sealed envelope technique: group M (Macintosh direct laryngoscope), group D (C-MAC D-Blade videolaryngoscope) and group F (flexible intubation video endoscope, FIVE).

A rigid cervical collar was applied while in sitting position to fit tightly without impairing proper ventilation and keeping the neck adjusted in a neutral position. Patients were placed supine afterwards. Standard monitoring was applied, using the multichannel monitor (MEC-2000; Mindray, Shenzhen, China). Patients were premedicated by 0.01 mg/kg atropine and 2 mg midazolam intravenously 3–5 min before induction of anaesthesia. After preoxygenating with 100% oxygen by face mask for 3–5 min, anaesthesia was induced using fentanyl 1 μg/kg, propofol 2 mg/kg and rocuronium 0.6 mg/kg, intravenous. IPPV was initiated for at least 90 s using isoflurane (1 MAC) in 100% oxygen. Laryngoscopy was carried out using Macintosh direct laryngoscope (group M), C-MAC D-Blade videolaryngoscope (group D) or FIVE (group F). One anaesthetist performed all laryngoscopies to minimize interoperator variability.

C spine movement was recorded with continuous fluoroscopy at 3–8 frames/s using a digital videofluoroscopy unit (BV Endura mobile C-arm with vascular package; Philips Medical Systems Nederland B.V., Eindhoven, The Netherlands) during both laryngoscopy and intubation. The entire time interval was recorded to capture the maximal extent of C spine movement. The C-arm of the fluoroscope was centred on the C spine and adjusted to include the occiput (Occ) and the fifth cervical vertebra (C5) in the lateral view before induction of anaesthesia. The Digital Imaging and Communications in Medicine images following the fluoroscopic video were analysed frame by frame using a dedicated workstation to determine the point of maximum change in angulation and to measure the relative change in angulation between C spine vertebrae. The vertebral reference lines for measuring movement of the C spine were selected in accordance with similar investigations described in the literature [5],[18],[19] − Occ (McGregor line): the line between the posterior margin of the hard palate and the opisthion (the midpoint on the posterior margin of the foramen magnum); C1: the line passing through the anterior and posterior arches of the Atlas More Details; and C2, C3, C4, C5: the imaginary lines running between the anterior inferior and the posterior inferior margins of the respective vertebral bodies. If anatomical variations or limitations in fluoroscopic visualization prevented the use of standard reference points, the radiologist, case by case, determined alternative reference points, remaining consistent for a given subject.

The following parameters were evaluated: age and BMI (kg/m2). The AWS was calculated for each patient using El-Ganzouri multivariate risk index [15],[16],[17]. Heart rate (HR) and mean arterial blood pressure (MABP) were measured preoperatively, after induction of anaesthesia, after ETT insertion and 5 min after ETT insertion. Laryngeal view grade, time to successful ETT insertion and the maximum change in angulation from baseline between Occ–C1, Occ–C2 and Occ–C5 were measured for each device and compared.

Statistical analysis

Data were fed to the computer and analysed using IBM SPSS software package, version 20.0 [20]. Qualitative data were described using number and percent. Quantitative data were described using range (minimum and maximum), mean±SD and median. Significance of the obtained results was judged at the 5% level [21]. χ2-Test was used for categorical variables; Fisher’s exact or Monte Carlo correction was used for correction for χ2 when more than 20% of the cells have expected count less than 5; F-test (analysis of variance) was used for normally quantitative variables, to compare between more than two studied groups, and post-hoc test (least significant difference) was used for pairwise comparisons; analysis of variance with repeated measures was used for normally quantitative variables, to compare between more than two periods or stages, and post-hoc test (least significant difference) for pairwise comparisons; Mann–Whitney test was used for abnormally quantitative variables, to compare between two studied groups; Kruskal–Wallis test was used for abnormally quantitative variables, to compare between more than two studied groups. And Wilcoxon’s signed-ranks test was used for abnormally quantitative variables, to compare between two periods.

Results

The three studied groups were matching as regards age, BMI and AWS. There were no significant differences in HR and MABP observed when comparing the three studied groups preoperatively, after induction and 5 min after ETT insertion. After insertion of the ETT, there were statistically significant increases in mean observed HR and MABP in group M compared with groups D and F, whereas there were no significant differences in mean observed HR and MABP between groups D and F at all time intervals. The Macintosh (group M) had significantly higher C and L grades than the two other devices in groups D and F (P=0.001, 0.001). No significant differences in C and L grades were attainted by the D-Blade in group D and the FIVE in group F (P=1) ([Figure 1]). D-Blade had a significantly shorter mean intubation time compared with Macintosh and FIVE (P=0.008 and 0.001, respectively). FIVE had a significantly longer mean intubation time compared with Macintosh (P<0.001) ([Figure 2]). The maximum angulations measured in group F were significantly lower than angles in groups M and D at Occ–C1 (P<0.001 and <0.001), at Occ–C2 (P<0.001 and <0.001) and at Occ–C5 (P<0.001 and <0.001). The maximum angulations measured in group D were significantly lower than angles in group M at Occ–C1 (P<0.001), at Occ–C2 (P<0.001) and at Occ–C5 (P<0.001) ([Figure 3],[Figure 4],[Figure 5],[Figure 6]).

Intubation is known to cause an exaggerated haemodynamic response in the form of tachycardia, hypertension and dysrhythmias. HR and MABP measured after insertion of the ETT in group M were significantly higher than in groups D and F. Meanwhile, there were no statistically significant differences in measured HR and MABP at different interval times between groups D and F. The Macintosh laryngoscope may increase the incidence of hypertension because it requires forced alignment of the oral and pharyngeal axes to view the glottis. This manoeuvre stimulates supraglottic regions and the oral tissue and induces the patient’s sympathetic response. It is a primary cause of an excessive haemodynamic response when the direct laryngoscopy technique is used. The use of a rigid cervical collar may reduce cervical spine movement, but it significantly reduces the mouth opening, making laryngoscopy difficult, and lifts the chin and calls for more force to view the glottis. Consequently, any technique for intubation that requires lesser lifting force would proportionally reduce the sympathetic discharge, and hence changes in HR and blood pressure. Indirect laryngoscopy results in less haemodynamic alteration than direct laryngoscopy, probably because less force is applied to the base of the tongue [22]. Excessive stimulation of a supraglottic region during intubation can be avoided, as alignment of the oral, pharyngeal and tracheal passages is not needed [23]. Coinciding with our results, direct laryngoscopy showed significantly higher cardiovascular changes when compared with videolaryngoscopes such as McGrath videolaryngoscope [23], Pentax (AWS) [24], Airtraq [25],[26] and Glidescope [27]. Also in agreement with our results, Gill et al.[28] investigated the haemodynamic response to intubation using FIS and McCoy laryngoscope in the presence of rigid cervical collar. HR and blood pressure increased significantly above preoperative values in the McCoy group as compared with the FIS group. In contrast to our results, Sarkilar et al.[29] found no differences in the haemodynamic responses to ETT performed with videolaryngoscopy and direct laryngoscopy in patients scheduled for major cardiac surgery. This was attributed to the anaesthetic agent combination. This study has been conducted in heterogeneous cardiac surgical patients with varied cardiac pathology coming for CABG, valvular surgeries and so on. The patients were on drugs such as beta blockers, which itself would have influenced the degree of haemodynamic response to ETT.

The D-Blade and the FIVE had significantly lower C and L grades than Macintosh. Meanwhile, there was no significant difference in C and L grades attainted by the D-Blade in Macintosh and the FIVE. Glottic visualization using Macintosh direct laryngoscope requires a direct line of sight obtained by forced alignment of the oral, pharyngeal and laryngeal axes. The use of cervical collar to simulate cervical immobilization decreased the mouth opening and limited neck movement, making glottic visualization via direct laryngoscopy even more difficult. However, this was not the issue for the D-Blade as laryngeal view is generated indirectly with a wide-view-angle camera mounted near the blade tip focused at the laryngeal inlet. Alignment of the oral, pharyngeal and laryngeal axes (i.e. a line of sight) is not essential to view the glottis. The distal part of the D-Blade is angulated with a sharp anterior deflection. This focuses the camera towards the larynx, giving a better view even in anterior or high larynx, whereas FIVE manoeuvred around the airway anatomy to access the vocal cords. Recently, Suppan et al.[30] systematically reviewed the evidence from randomized controlled trials comparing alternative intubation devices with the standard Macintosh laryngoscope in subjects with cervical spine immobilization using the MILS technique, head immobilization by fixation of at least two points or a cervical collar. Fifteen studies (1684 patients) have reported on the C and L grade. On average, 66% of patients had C and L grade 1 with alternative devices compared with 18% with Macintosh laryngoscopy. Sufficient data to perform meta-analyses were available for five devices, the Airtraq, Airway scope, C-Mac, Glidescope and McGrath, and all were associated with a significantly higher rate of C and L grade 1 compared with Macintosh laryngoscopy. Also in agreement with our results, Yumul et al.[31] compared the C-MAC videolaryngoscope with the standard FIS for intubation of patients undergoing cervical spine surgery with MILS. There were no significant differences in both the C and L grades and percentage of glottic opening (POGO).

D-Blade had a significantly shorter mean intubation time compared with Macintosh and FIVE (P=0.008 and 0.001, respectively). FIVE had a significantly longer mean intubation time compared with Macintosh (P<0.001). D-Blade does not require alignment of the airway axes, because the glottic view is readily obtained by means of a wide-view camera positioned near the blade tip. Therefore, seeing vocal cords in a monitor facilitates the intubation process and reduces intubation time. In addition, using a malleable stylet moulded on the D-Blade made ETT passage between the cord easier and faster. FIVE took more time to be manoeuvred around airway anatomy to access the vocal cords. In agreement with our results, Yumul et al.[31] compared the C-MAC videolaryngoscope with the standard FIS for intubation of patients undergoing cervical spine surgery with MILS. They found that the use of the C-MAC facilitated a more rapid tracheal intubation compared with the FIS. It was attributed to the fact that the C-MAC requires virtually no set up time and is less susceptible to fogging. However, Akbar et al.[32] compared tracheal intubation using the C-MAC videolaryngoscope and Macintosh laryngoscope in patients during MILS. C-MAC videolaryngoscope had a significantly shorter time to intubate compared with Macintosh laryngoscope.

Cervical spine motion during intubation in group F was significantly less than motion in groups M and D at all studied motion segments. whereas cervical motion measured in group D was significantly less than in group M at all motion segments. Direct laryngoscopy and intubation using a Macintosh blade requires alignment of the oral, pharyngeal and laryngeal axes to achieve a line of sight. In contrast, the D-Blade does not require alignment of the oral, pharyngeal and tracheal axes, because the laryngoscopic view is obtained from a camera positioned at ∼3.5 cm from the blade tip, whereas FIVE manoeuvred around airway anatomy to access the vocal cords. Movement occurs because of associated manoeuvres commonly used to enlarge the posterior pharyngeal space, such as jaw thrust and tongue pull. Maruyama et al.[19] compared upper cervical spine movement during intubation using Pentax AWS, McCoy and Macintosh in elective patients with normal spine. They found that Pentax AWS produced significantly less movement of upper C spine (Occ–C4) for intubation in patients with normal C spine than Macintosh or McCoy laryngoscope. In addition, Maruyama et al.[18] studied C spine motion with the Pentax AWS or Macintosh laryngoscope in patients with normal spine with MILS to simulate unstable spine. They found that Pentax AWS significantly decreased median movement of the C spine at the Occ–C1, C1–C2 and C3–C4, resulting in a significant decrease in cumulative (Occ–C4) upper C spine movement. Laosuwan et al.[33] found that the cervical motion during intubation at C3/4 and the cumulative changes of all cervical spine levels, measured by cinefluoroscopy, with the McGrath Series 5 were less than with the Macintosh laryngoscope. Coinciding with our results, Wong et al.[5] studied cervical spine motion during FIS compared with the Lo-Pro GlideScope in 28 healthy adults requiring intubation for radiographic procedures under general anaesthesia with no cervical immobilization. They found that FIS resulted in less cervical extension compared with GlideScope for every angle calculated, statistically significant between Occ–C1, Occ–C2 and Occ–C4. They also found that airway manoeuvres performed before FIS such as jaw thrust and tongue pull resulted in cervical spine movement. However, when Sahin et al.[34] compared upper C spine extension during intubation using direct laryngoscopy, intubating LMA and FIS, there was significantly less movement with FIS compared with direct laryngoscope.

Also in agreement with our results, Turkstra et al.[35] compared between the Airtraq and Macintosh laryngoscopes regarding cervical motion during intubation with MILS. They found that C spine motion using the Airtraq was less than that during Macintosh laryngoscopy, averaging 66% less at three of the motion segments studied: Occ–C1, C2–C5 and C5–thoracic. There was no difference at the C1–C2 segment. In addition, Turkstra et al.[36] studied C spine motion during laryngoscopy with Shikani Optical Stylet (SOS) and conventional Macintosh blade. The C spine motion was examined at the Occ–C1, C1–C2, C2–C5 and C5–thoracic motion segments. They found that C spine motion was 52% less at three of the motion segments studied, Occ–C1, C2–C5 and C5–thoracic. when comparing SOS versus Macintosh laryngoscopy. Turkstra et al.[37] also compared between Trachlight, GlideScope and Macintosh laryngoscope regarding cervical motion during intubation with MILS. C spine motion was examined at Occ–C1, C1–C2, C2–C5 and C5–thoracic motion segments during manual ventilation via bag-mask, laryngoscopy and intubation. GlideScope reduced C spine motion at C2–C5 segment by 50% compared with Macintosh laryngoscope. Trachlight reduced C spine motion at all measured motion segments.

Similar to our results, Hirabayashi et al.[38] compared cervical spine movement during laryngoscopy using the Airtraq or Macintosh laryngoscopes. The Airtraq achieved 29% less cervical spinal extension than that measured during Macintosh laryngoscopy between Occ and C4. Also Hirabayashi et al.[39] investigated cervical spine movement during laryngoscopy using the Pentax AWS compared with the Macintosh laryngoscope. They found that the cervical movement between Occ–C4 during the Pentax AWS was 39% less than that during the Macintosh laryngoscopy. The movement of the atlanto-occipital distance using the Pentax AWS was 42% less than that during laryngoscopy using the Macintosh laryngoscope. However, Kill et al.[40] used video motion analysis to measure the maximum extension angle caused by GlideScope compared with conventional laryngoscopy in anaesthetized patients with unsecured cervical spines. They found that GlideScope significantly reduced movements of the C spine in patients with unsecured C spines.